pgsql: Factor error generation out of ExecPartitionCheck.

Factor error generation out of ExecPartitionCheck.

At present, we always raise an ERROR if the partition constraint
is violated, but a pending patch for UPDATE tuple routing will
consider instead moving the tuple to the correct partition.
Refactor to make that simpler.

Amit Khandekar, reviewed by Amit Langote, David Rowley, and me.

Discussion: http://postgr.es/m/CAJ3gD9cue54GbEzfV-61nyGpijvjZgCcghvLsB0_nL8Nm8HzCA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/19c47e7c820241e1befd975cb4411af7d43e1309

Modified Files
--------------
src/backend/commands/copy.c | 2 +-
src/backend/executor/execMain.c | 107 +++++++++++++++++++--------------
src/backend/executor/execPartition.c | 5 +-
src/backend/executor/execReplication.c | 4 +-
src/backend/executor/nodeModifyTable.c | 4 +-
src/include/executor/executor.h | 7 ++-
6 files changed, 74 insertions(+), 55 deletions(-)